Method of explosively plugging a leaky metal tube in a heat exchanger tube bundle

ABSTRACT

THIS INVENTION PROVIDES AN EXPLOSIVE PLUGGING DEVICE FOR INSERTION INTO A LEAKY METAL TUBE OF A HEAT EXCHANGER BUNDLE TO PLUG THE TUBE BY EXPLOSIVE WELDING AND A METHOD OF EXPLOSIVELY WELDING A METALLIC PLUGGING DEVICE HAVING AN EXPLOSIVE CHARGE TO A METAL TUBE BY DETONATING THE CHARGE WITH A DETONATION INITIATOR TO PERIPHERALLY EXPAND THE PLUG INTO WELDING ASSOCIATION WITH THE TUBE.

Jan. 19, 1971 BROWN ET AL 3,555,656

METHOD OF EXPLQSIVLLY PLUGGING A LEAKY METAL TUBE IN A HEAT EXCHAN TUBEBUNDLE v Filed May 1967 FIG.|.

WQIITNESSES INVENTOR 57 5: BY QQSL H W WZQU R V 7 I w \L\\\\\\E i- 9United States Patent 3,555,656 METHOD OF EXPLOSIVELY PLUGGING A LEAKYMETAL TUBE IN A HEAT EXCHANGER TUBE BUNDLE Francis X. Brown, Broomal,and Samuel W. Wismer, Jr., Springfield, Pa., assignors to WestinghouseElectric Corporation, Pittsburgh, Pa., a corporation of PennsylvaniaFiled May 25, 1967, Ser. No. 641,381 .Int. Cl. B22d 19/10; B23p 7/00U.S. Cl. 29-401 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THEINVENTION The invention relates to a method and device for pluggingleaky tubes in heat exchangers of the tube and shell type and has for anobject to provide a method and device of the type that provides apositive, metallurigcally bonded seal that is leak-proof when exposed topressurized fluids, and that is relatively safe and expeditions toemploy in all types of tube and shell type heat exchangers such ascondensers, feed Water heaters and steam generators.

Heat exchangers of the above type are employed to transfer heat from onefluid to another and are usually provided with a bundle of tubes, theopen ends of which extend through a suitable tube sheet disposed withina suitable channel head to which one of the fluids is directed forcirculation through the tubes. The tube bundle and tube sheet areencompassed by a shell structure through which the other fluid iscirculated in a manner to pass over the outer surfaces of the tubes. Oneof the fluids is hotter than the other, hence during operation thecooler fluid is heated by transfer of heat from the hotter fluid, andvice versa.

Usually one or both of the fluids are pressurized and, to preventintermingling of the two fluids, the ends of the tubes are welded orotherwise sealingly secured to the tube sheet.

4 However, in operation, a tube may spring a leak through its wall or aleak may develop at the tube-to-tube sheet seal, thereby causingundesirable flow of the more highly pressurized fluid into the lowerpressure fluid and contamination or adulteration of the lower pressurefluid.

Many solutions have heretofore been proposed to block or plug such aleaky tube at both ends, thereby to inactivate the tube and terminatesuch leakage. Such solutions have usually involved mechanicallyexpansible plugs for insertion in the leaky tube. Such solutionsnecessarily required a workman to be in close proximity with the tubesheet in order to make such repair and entailed working entirely withinthe channel head, in the larger industrial heat exchangers of the typesmentioned above. Also, such prior plugging arrangements were subject toincipient leakage leading to corrosion and eventually even catastrophicfailure after prolonged service.

SUMMARY Briefly, one aspect of the invention resides in the provision ofan explosive plugging device for insertion into a metal tube to plugsaid tube by explosively welding of the plugging device to the tube. Inaccordance with the in- Patented Jan. 19, 1971 vention the pluggingdevice comprises a cylindrical body formed to be slidably inserted intothe tube and having a solid cylindrical portion to block the flow offluid and a hollow cylindrical portion containing an explosive chemicalcharge which is detonated by a suitable explosive initiator toperipherally expand the hollow cylindrical portion into violent abutmentwith the inner wall of the tube with attendant welding or metallurgicalbonding, thereby effecting a positive leak-proof seal.

Explosive welding techniques are generally known in the welding art andmany schemes have been employed or proposed to solve specific problemsin the manufacture of heat exchange apparatus, as indicated in C. C.Simons and R. I. Carlson patent application No. 467,244, filed June 28,1965, now Pat. No. 3,409,969, and R. J. Carlson, C.C. Simons and R. L.Bradford patent application No. 488,670, filed Sept. 20, 1965 and nowPat. No. 3,402,870. Both of these applications are assigned to the sameassignee as this invention and more fully describe the phenomenaattendant in explosive welding.

Another aspect of the invention resides in a method of explosivelywelding a plugging device of the above type in a leaky tube of a tubeand shell heat exchanger. Briefly the method comprises insertion of a.plugging device of the above type into the leaky tube within the lengthof the tube confined in the tube sheet but preferably in close proximitywith the open end of the tube and detonating the explosive charge toeflect the peripheral welded seal. The detonation is effected preferablyfrom a position external of the heat exchanger channel head, therebyrendering the method inherently safe for personnel, especially inrepairing nuclear power steam generators.

The above method is subject to modification involving chamfering of theend of the tube and adjacent tube sheet and emplacement of the pluggingdevice in flush relation with the surface of the tube sheet, so that, ondetonation of the explosive charge, a portion of the plugging device isexpanded into the flared opening formed by the chamfermg.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial sectional view of atypical heat exchanger of the tube and shell type prepared for theplugging of a leaky tube, in accordance: with the invention;

FIG. 2 is an enlarged axial sectional view of an explosive tube pluggingdevice in accordance with the invention;

FIG. 3 is an enlarged fragmentary axial sectional view illustrating theplugging device in inserted position within a leaky tube of the heatexchanger shown in FIG. 1, in preparation for sealing by welding;

FIG. 4 is a view similar to FIG. 3 but illustrating the tube and plugafter welding;

FIG. 5 is a fragmentary axial sectional view illustrating another leakytube condition;

FIG. 6 is a view similar to FIG. 5 but illustrating preparation of thetube and tube sheet for plugging;

FIG. 7 is a view similar to FIG. 2 but illustrating a further pluggingdevice modification;

FIG. 8 is a view illustrating the modified plugging device of FIG. 7inserted in the prepared tube of FIG. 6, in preparation for welding; and

FIG. 9 is a view similar to FIG. 8 but illustrating the tube and plugafter welding.

DESCRIPTION OF THE INVENTION Referring to the drawings in detail, inFIG. 1 there is shown a typical heat exchanger 10 of the tube and shelltype comprising the usual components, as follows a bundle of tubes 12 ofthe hairpin type having their opposite end portions 14 and 15 extendingthrough a suitable tube sheet 16.

As illustrated, the tube sheet 16 may be of the clad type, including arelatively thick plate portion 17 of one type of metal and a relativelythin clad layer 1 8 of a different type of metal. As more fullyexplained in F. X. Brown and L. K. Poole Pat. 3,257,710, issued June 28,1966, and assigned to the same assignee as this invention, the metal forthe clad layer 18 may be selected for weld compatibility with the metalof the tubes 12, to permit welding of the tube end portions 14 and 15 tothe tube sheet 16, as more clearly shown at 19 in FIG. 3.

The tube bundle 12 is enclosed by a tubular shell structure 20 disposedin fixed sealing abutment along its peripheral end portion with theperiphery of the tube sheet 16 and jointly therewith forming a chamber21. The shell 20 has a fluid inlet opening 22 and a fluid outlet opening23 communicating with the chamber 21.

A channel head 24 having a partition 25 is disposed in fired peripheralsealing abutment with the opposite face of the tube sheet 16 and jointlytherewith forms an inlet chamber 26 in communication with the tube endportions 14 and an outlet chamber 27 in communication with the tube endportions 15. The channel head 24 has a fluid inlet opening 28communicating with the chamber 26 and a fluid outlet opening 29communicating with the chamber 27.

In operation, as well known in the art, pressurized fluid at onetemperature is admitted to the channel head chamber 26 through the inlet28 and directed through the bundle of tubes 12 to the chamber 27 andthence directed through the outlet 29. A second fluid at a differenttemperature and pressure is directed into the chamber 21 through theinlet 22 and thence through the outlet 23. During its flow across theouter surfaces of the tubes 12, heat is exchanged between the two fluidswith resulting heating of one fluid and cooling of the other.

Since the heat exchanger described above employs different fluids atdifferent pressures, it is desirable, and in many cases imperative, toprevent intermingling of the two fluids. This is especially so in heatexchangers such as steam generators employed in nuclear turbine powerplants, since the fluid flowing through the tubes 12 is usually thehotter fluid and has been heated in the nuclear reactor, and thereforemay contain some radioactivity.

Accordingly, if leaks should occur in the tubes, it is present practiceto interrupt operation of the heat exchanger 10 and plug both ends 14and 15 of a tube 12 that is leaking fluid.

In accordance with the invention, there is provided an explosiveplugging device 30, as best shown in FIG. 2, for insertion into a tube12 that is leaking through a rupture 31 in the tube wall as indicated inFIG. 3, and a method of plugging the leaky tube in a positive leakproofmanner.

The plug device is of symmetrical circular crosssection about itslongitudinal axis A-A and includes a metallic body member 33 preferablyformed of metal having weld compatibility with the tube metal, and ofgenerally thimble form having one end portion 34 of solid cylindricalshape and an opposite end portion 35 of hollow cylindrical shape jointlyforming an axial cavity 36 of cylindrical shape. As shown in FIGS. 2 and3 the solid portion 34 is of such a diameter as to permit a slidable fitwith the tube end 14 to be plugged, while the hollow portion 35 is ofsmaller diameter than the solid portion and of about the same wallthickness as the tube.

More specifically the solid portion 34 is on the order of about .002"smaller diameter than the internal diameter of the tube end 14, whilethe hollow portion 35 is on the order of about .0 30.050 smallerdiameter than the diameter of the solid portion to provide an annularstand-off distance or space S of about .015"- .025" from the internalwall of the tube end 14.

Within the cavity 36 there is received an explosive chemical charge 37of cylindrical shape and provided with an axial opening 38. The charge37 is preferably of integral or cast form and extends axially about 50%of the length of the cavity. The charge may be of any suitable highdetonation velocity, explosive material for example, TNT(trinitrotoluene) or PETN (pentaerythritol tetranitrate) and of suchaxial length and cross-sectional area as to provide about 6 grams persquare inch (of cross-sectional area) of such explosive.

An end cap member 40 of any suitable plastic material having an axialopening 41 extending therethrough is provided with an inner end portion42 of a diameter to be snugly received in the cavity 36 and maintain thecharge 37 in position and an outer end portion 43 of about the samediameter as the outer diameter of the tube end portion 14.

An electrical detonation initiator 44 of cylindrical form and having apair of external lead wires 45 is slidably received in the registeringaxial openings 41 and 38 and extending through the charge 37 intoendwise abutment With the end Wall of the cavity 37.

The explosive plug device 30 is inserted into the tube end portion 14 tothe fullest extent permitted by abut-.

ment of the end portion 43 of the cap member 40 with the end of the tubeportion 14. Accordingly, the body member 33 and the explosive charge 37are properly positioned within the tube portion in the optimum positionindicated in FIG. 3.

The lead wires 45 are then connected to a supply of electrical currentand energized to fire the initiator 44, which, in turn detonates theexplosive charge 37. As the charge 37 is detonated, its explosive forcesexplosively expand the hollow end portion 35 of the body in peripherallyoutward direction across the annular stand-off space S into impingingabutment with the inner wall of the tube portion 14, as shown in FIG. 4.The velocity of radially outward movement of the end portion 35 is ofsuflicient magnitude to metallurgically bond or explosively weld theperiphery of the hollow end portion 35 to the inner periphery of thetube and provide a seal that is leak-proof and reliable, even whensubjected to fluid pressure, as incurred in operation of the heatexchanger.

Any refuse remaining in the cavity 36 from the detonated explosive, theplastic cap member 40 or the initiator 44 may be easily removed.

The opposite end portion 15 of the leaky tube may be plugged in the samemanner described above to completely isolate the tube from the system.

In FIG. 5, there is shown a tube end portion 14a, similar to the tubeend portion 14 shown in FIGS. 3 and 4, and extending through the tubesheet 16. In this case the tube has not been ruptured, but the annulartube-totube sheet weld joint 19 has incurred a small break causing aleakage flow path 31a to to be established between the outer surface ofthe tube and the tube sheet, so that fluid in the chamber 21 and thefluid in chamber 26 may intermingle.

The above type of leaky tube may be plugged in the same manner describedin conjunction with FIGS. 2-4, incl., since the explosive forces of thecharge 37 are so great that a peripheral portion of the tube and 14awill be expanded into tight abutment with the tube sheet to interruptthe flow path 31a. However, a positive and reliable seal may not beobtained in every instance, since most of the explosive force may beabsorbed in Welding the plug body 33 to the tube.

Accordingly, in cases of leakage as shown in FIG. 5, there is provided amodified explosive plugging device 50', shown in FIGS. 7 and 8. Thisplugging device may be identical in all aspects to the plugging device30, except that the end cap 51 has an outer end portion 52 of greaterdiameter than the end portion 43 for a purpose subsequently to bedescribed.

As shown in FIG. 6, the preparation for plugging the tube end portion141: comprises the step of machining away (by chamfering orcountersinking, for example) a portion of the tube, the weld joint 19and a peripheral portion of the clad layer 18 surrounding the tube toprovide an enlarged opening 53 that is flared or beveled at any suitableangle on. The machining is performed to a depth sufficient to cause theend 54 of the tube to terminate within the clad layer 18 and present aflush continuation of the flared opening 53.

To plug the tube end portion 14a, the plug 50 is inserted thereinto tothe fullest extent permitted by the end cap 51. The end portion 52 isformed with a larger diameter than the maximum diameter of the flaredopening, so that insertion of the plug is limited by abutment of the endportion 52 with the outer surface 56 of the tube sheet. Accordingly, asin the first embodiment, the plug body 57 and the explosive charge 58are properly located in the optimum position.

After, the explosive charge is detonated, the plug body 57 isexplosively deformed as shown in FIG. 9 to form an annular explosiveweld or metallurgical bond between the periphery of the hollow tubularbody portion 59 and the peripheral surface of the flared opening in thetube sheet, thereby effectively interrupting the leakage path 31a.

It will now be seen that the invention provides a simple, yet highlyeifective method and apparatus for plugging a leaky heat exchanger tubeby explosively welding the plug in position.

It must be pointed out that in both disclosed schemes, the pluggingdevice is positioned in the leaky tube within the confines of the tubesheet 16. Accordingly, the large mass of the tube sheet is eflective togreatly restrain the explosive forces of the exploding charge andenhance the explosive welding effect.

Also, since the tube portion subjected to the explosive forces is notgreatly enlarged in cross-section, due to the restraining effect of thetube sheet, the plugged tube may be readily removed at a later date andreplaced in any conventional manner, if so desired.

It will further be seen that since the lead wires 45 may be passedthrough the inlet or outlet openings 28 or 29, or a suitable man-wayopening (not shown), the tube plugging may be conducted in a manner safeto personnel.

We claim:

1. The method of plugging a leaky metal tube in a heat exchanger tubebundle and tube sheet structure, wherein the open ends of the tubes inthe tube bundle extend through said tube sheet, said method comprisinginserting a metallic plug device having an explosive charge into theopening end of said leaky tube, inserting a detonation initiator intosaid plug in axial juxtaposition with said eXposive charge, and

firing said initiator to detonate said charge in a manner toperipherally expand said plug into peripheral welding association withsaid tube.

2. The method recited in claim 1 and further includchamfering the openend of said leaky tube to provide a flared opening in the tube sheetsurface, and

positioning the metallic plug device adjacent said flared opening beforedetonation of the initiator, thereby to peripherally expand an annularportion of the plug device into welding association with said flaredopening.

3. The method recited in claim 1 wherein the tube sheet is clad with alayer of metal having weld compatibility with the metal tubes, and

the metallic plug device is formed of metal having weld compatibilitywith the metal tubes and/or said layer of metal.

4. The method recited in claim 1, wherein the tube sheet is clad with alayer of metal having weld compatibility with the metal tubes, and themetallic plug device is formed of metal having weld compatibility withthe metal and! or said layer of metal, and including chamfering the openend of said leaky tube to provide a flared opening in said layer ofmetal, and

positioning the metallic plug device in substantially flush relationwith said layer of metal, thereby to peripherally expand an annularportion of the plug device into welding relation with said flaredopening.

References Cited UNITED STATES PATENTS FOREIGN PATENTS l/l957 England29-421 PAUL M. COHEN, Primary Examiner US. Cl. X.R.

